Acrania vs. Craniata

Acrania and Craniata Definitions
Acrania
(physiology) Partial or total absence of the skull.
Craniata
Fishes; amphibians; reptiles; birds; mammals
Acrania
Partial or total absence of the skull.
Acrania
The lowest group of Vertebrata, including the amphioxus, in which no skull exists.